Storage of liquefied gases



Nov. 8, 1960 T. J. WEBSTER STORAGE 01-" LIQUEFIED GASES Filed June 19. 1958 Inventor TH MAS I HN WEBST R Q By aw Attorney United States Patent STORAGE OF LIQUEFIED GASES Thomas John Webster, Middlesex, England, assignor t The British Oxygen Company Limited, a British com- P y This invention relates to the storage of liquefied gases, and while not limited to such application is particularly applicable to the storage of liquid oxygen in a tank associated with a rocket motor. In the field of rocket practice it is frequently necessary for economy of weight to store liquid oxygen in an unlagged tank, and to transfer it through unlagged lines to unlagged pumps.

Lagging of storage, transfer, and pumping equipment for liquefied gases, the boiling points of which are much below atmospheric temperatures, is now a well-established practice, the technique adopted in any particular case beingdictated by factors of economy and the object being to minimise evaporation loss and to prevent the deposition of atmospheric moisture in the form of ice or frost on the exterior of the equipment. Despite the lagging of storage containers it is found that continuous topping up is necessary to compensate for evaporation losses caused by heat inleak, and in the'field of rocketry this complicates firing procedure, because a direct connection must be maintained between the storage tank of a rocket and an external liquid oxygen supplysource until almost the last moment before take-off.

Moreover there are inherent adverse effects connected with the storage of liquefied gases in non-insulated containers. In a typical rocket installation the liquid oxygen is exposed to a considerable hydrostatic head, particularly at the bottom of the standpipe between a rocket storage tank and its motor. In this instance the liquid oxygen can attain there a temperature above its normal atmospheric boiling point without gas evolution, as it is maintained at higher pressure. Irrespective of this higher pressure it attains lower density because of the increased temperature, and tends to rise if displaced by the upper layers of cooler and heavier liquid oxygen situated above. Consequently super-heated liquid oxygen rises and releases suddenly, by evaporation, the quantity of gas suflicient to lower its temperature to the level corresponding to the pressure prevailing in the upper layers. If a sufficient degree of super-heat builds up in the oxygen before it commences to boil, the phenomenon known as bumping can occur in vertical standpipes and storage vessels and this may submit the structure to considerable mechanical strain.

It is the object of this invention to provide means whereby ice formation on, and heat inleak into an unlagged vessel, line, pump or the like containing a liquefied gas, in particular liquid oxygen, can be suppressed without in any way adding to the Weight of the oxygencontaining equipment.

According to the present, invention the method of heatinsulating and preventing of ice formation on unlagged equipment which contains liquefied gas comprises spraying suitable liquefied gas onto the external surface of the equipment. Preferably the liquefied gas which sprayed onto the equipment is liquid nitrogen, in order to avoid any fire hazard.

The term suitable liquefied gas is intended to include gases or a mixture thereof which can be usefully employed to obtain the desired results, the greatest efficiency being obtained with a suitable liquefied gas having a boiling point as near as possible to, or lower than, the stored gas, but the term does not include liquefied fuel gas the use of which would be hazardous due to fire risk, nor other dangerous gases, such as those of a highly poisonous nature, the use of which would be absurd.

In the application of the invention to an unlagged storage container, the liquefied gas may be sprayed onto the external surface of the container over one or more zones, each of which encompasses an upper region of said sur face, so that liquefied gas and gas in the gaseous phase evaporated therefrom gravitate downwardly from said upper region over a lower region of the external surface of the equipment.

The application of the invention to the liquid oxygen storage tank of a rocket will now be described with reference to the accompanying drawings, which are diagrammatic, and in which:

Fig. l is a fragmentary side elevation of a rocket to which the method of the present invention is applied.

Fig. 2 is a plan view of Fig. 1.

Referring to the drawings, the rocket indicated at 10 has a liquid oxygen storage tank section 11 extending from the dotted line 12 to the dotted line 13, and liquid nitrogen is sprayed onto the external surface of said tank section 11, over a zone encompassing a top region of section 11, as inwardly-directed spray jets 14 issuing from a circle of piping 15. A second circle of piping 16 supplies inwardly-directed spray jets 17 onto the external surface of the tank section 11 over a second zone encompassing an upper region of the tank which is spaced downwardly from the top region, and is about half-way up the tank section 11. The rings of piping 15, 16 receive liquid nitrogen from respective feed pipes 18, 19, the latter being fed by pumps (not shown) from a liquid nitrogen storage tank or tanks (not shown).

The rings of piping 15 and 16 are shown diagrammatically and not in detail, but it will be appreciated that the rings could each be comprised of readily separable sections which can easily be assembled in position around the rocket or removed, and that they form part of a ground installation for effecting the spraying of the liquid nitrogen, so that they made no contribution to the weight of the rocket.

With the tank section 11 of the rocket 10 filled with liquid oxygen and the rocket in readiness for take-off, liquid nitrogen spraying from the pipe rings 15 and 16 maintains over the surface of the tank section 11 a constant covering of liquid gas and cold gas in the gaseous phase evaporated therefrom, due to the liquid nitrogen and cold evaporated nitrogen gas being more dense than the surrounding air so that they tend to gravitate down the surface of the section 11. The two pipe rings 15, 16 at different levels ensure complete coverage of a relatively long tank, but with a short tank a single pipe ring would sufiice, or three or more rings could be used for an even longer tank.

Obviously the form and shape of the spraying installation will be varied as necessary to suit any particular application, the spray installation shown in the diagram being only one example. Also indicated in Fig. l is ducting 20 and a fan 21 for removing cold nitrogen gas and mist from the base region of the tank section 11, but practical tests have suggested that this refinement can be dispensed with, since the amount of mist formed by the nitrogen sprays is not significantly greater than that evolved by an unsprayed tank containing boiling liquid oxygen.

As soon as the rocket is fired and liquid nitrogen spraying ceases, such little liquid nitrogen as is present on the external surface quickly evaporates, leaving nothing to add to the weight of the rocket.

The methodcompletely prevents ice formation on the walls of unlagged equipment containing liquefied oxygen and it completely restricts the ingress of heat into the equipment, thus ensuring that the temperature of the liquid oxygen does not exceed -183 :C. If desired, the liquid oxygen .can be cooled to and ,rnai'ntaincd at a temperature slightly below its normallboiling point (183 C.) by spraying slightly more liquid nitrogen on the equipment than is normally required to maintain full heat insulation. By eliminating the-evaporation of the liquid oxygen in a rocket the method enables the quantity of liquid oxygen charged to the rocket to be carefully adjusted to the desired amount Well before firing. All external liquid oxygen connections to the rocket can then be removed andthe rocket=can be kept in a state of readiness for an indefinite and prolonged period by operating the liquid nitrogen sprays. The method has many advantages over that involving the topping up of a rocket with liquid oxygen right up to the timeof firing, and'the fact that theoxygen is maintained at a temperature of at most -183 0., and if desired several degrees lower, prevents bumping and ensures a good start by avoiding the possibility of gas formation in the rocket pumps.

It will be appreciated that the invention can be employed to overcome all the undesirable features hitherto encountered in the storage and transfer of liquefied gases in lagged equipment and enables costly and heavy lagging to be dispensed with, and whereas the employment of liquid nitrogen is specifically referred to for the spray- 1ng,-it is envisaged that other suitable liquefied gases, erg. liquid oxygen or liquid air, could be employed under conditions favourable to their use.

I claim:

-1. Process for maintaining a cold body of low-tem perature liquefied gas at a temperature not exceeding its atmospheric boiling point while said liquefied gas is stored in an unlagged tank with the tank in an environment of ambient atmosphere, comprising continuously spraying a suitable liquefied gas onto the external surface of said unlagged tank at such a rate as to encompass said surface with an effective heat-insulating covering consisting of the last-mentioned liquefied gas and cold gas in the gaseous phase evaporated therefrom.

2. Process for maintaining a. cold body of low-temperature liquid oxygen at a temperature not exceeding its atmospheric boiling point While said liquid oxygen is stored in an unlagged tank with the tank in an environment of ambient atmosphere, comprising continuously spraying liquid nitrogen onto the external surface of said unlagged tank at such a rate as to encompass said surface with an effective heat-insulating covering consisting of liquid nitrogen and cold nitrogen in the gaseous phase evaporated therefrom.

3. Process for maintaining a cold body of low-temperature liquid oxygen at a temperature not exceeding its atmospheric boiling point while said liquid oxygen is stored in an unlagged tank and ancillary equipment of a rocket which is being held in readiness for launching in an environment of ambient atmosphere, comprising continuously spraying liquid nitrogen onto the external surface of said unlagged tank and ancillary equipment at such a rate as to encompass said surfacewith an effective heat insulat-ing covering consisting of liquid nitrogen and cold nitrogen in the gaseous phase evaporated therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 1,680,873 Lucas-Girardville Aug. 14, 1928 2,447,249 Hill Aug. 17, 1948 2,480,472 Jackson Aug. 30, 1949 2,670,605 Van Zandt et a1 Mar. 2, 1954 2,711,882 Narbutovskih June 28, 1955 2,784,567 Reynolds Mar. 12,1957 2,798,364 Morrison July 9, 1957 

